ABSTRACT

A previous study of the aerotolerant bacterium Lactobacillus plantarum, which lacks superoxide dismutase (SOD), demonstrated that it possesses a novel substitute for this defensive enzyme. Thus, L. plantarum contains 20 to 25 mM Mn(II),m in a dialyzable form, which is able to scavenge O2- apparently as effectively as do the micromolar levels of SOD present in most other organisms. This report describes a survey of the lactic acid bacteria. The substitution of millimolar levels of Mn(II) for micromolar levels of SOD is a common occurrence in this group of microorganisms, which contained either SOD or high levels of Mn(II), but not both. Two strains were found which had neither high levels of Mn(II) nor SOD, and they were, as was expected, very oxygen intolerant. Lactic acid bacteria containing SOD grew better aerobically than anaerobically, whereas the organisms containing Mn(II) in place of SOD showed aerobic growth which was best, at best, equal to anaerobic growth. Plumbagin (5-hydroxy-2-methyl-1,4-naphthoquinone) increases the rate of O2- production in these organisms. Lactobacillus strains containing high intracellular Mn(II) were more resistant to the oxygen-dependent toxicity of plumbagin than were strains containing lower levels of Mn(II). The results support the conclusion that a high internal level of Mn(II) provides these organisms with an important defence against endogenous O2-.